I thought we were talking about what you first say in your help file / documentation. If someone asks a pre-sales question, it's appropriate to say "thanks for your interest in my item", but when people are writing for support, they don't really want to be thanked.. they want support!
You're right, we talking about what to say in help file. I just gave him a tip, about the time when he can contact his customers. However, sometimes customers will contact you to simply thank you for the awesome item that you've created.